The present invention relates to a method for collecting continuously particle component in the aqueous solution without using filters and/or centrifuge separators. The method utilizes a phenomenon that particle component in the aqueous solution aggregates at the liquid-to-liquid interface between the aqueous solution (aqueous phase) containing the particle component as the target component and the solvent (solvent phase) having hydrophobic nature and not mixing with water.
Liquid-liquid extraction method (solvent extraction method), by which the target component included in the aqueous solution may be extracted into the solvent (such as organic solvent) that contains extraction agents (extractants) having hydrophobic nature and does not mix with water, is widely used in various industrial fields such as metal refinement, nuclear fuel reprocessing, removal of harmful ingredients in the waste water, recycling by separation and recovering of commercially valuable materials. As for the method for extracting the component in the aqueous solution other than liquid-liquid extraction method, there is another method designed “liquid-to-solid extraction method” which uses solid materials such as resin to be filled into the column and the like structure. Liquid-liquid extraction method, which is often regarded as not so simple as the column-type liquid-to-solid extraction method, is better than the liquid-solid extraction method in terms of extraction capacity and speed of extraction process. In order to extract efficiently the target component in the aqueous solution by applying liquid-liquid extraction, it is required to increase the dimension of the liquid-to-liquid interface by mixing fully the aqueous phase and the extracting solvent phase and thus to promote the interface reaction. In order to meet this requirement, typically, the material transport from one liquid to the other liquid is made reach an equilibrium state by keeping the emulsion state (the state in which the water and the organic solvent are well mixed and formed in emulsion) with continuous stirring and vibration (shaking) operations.
As for the apparatus for extracting the target component included in the aqueous phase into the extracting solvent phase by introducing continuously the aqueous phase and the extracting solvent phase at a constant flow rate, mixer-settler extractors using stirring machines come into wide use. Alternatively, relatively newly developed continuous liquid-liquid extraction apparatus such pulsed column using vibration due to pulse generation in order to disperse liquid drops, and centrifugal extractor for phase separation by using centrifugal forces (refer to JP 09-085120 A) are used in nuclear industries. Specifically, centrifugal extractors are expected to be applied to the reprocessing technology of spent nuclear fuels because they are excellent in the efficiency of the phase contact and the phase separation of the two liquid phases, and are compact in size.